The present invention relates generally to recombinant plasmids and, more specifically, to recombinant plasmids containing a DNA coding for human interferon-.beta. (referred to as IFN-.beta. hereinafter) and a process for producing IFN-.beta..
Expression of genes in organisms is achieved through a series of biological reactions involving synthesis of an RNA using a DNA as a template, i.e. the transcription step and synthesis of a polypeptide based on the information of mRNA, i.e. the translation step. Such recombinant DNA technology has now been developed to the extent that its industrial application has become possible.
In this connection, it is important to develop a method for the insertion of foreign genes into a plasmid vector for the efficient synthesis of the polypeptide coded by the foreign gene in a microorganism.
For the efficient expression of foreign genes in a microorganism, particularly in Escherichia coli, various attempts have heretofor been made. In order to increase the rate of transcription, lactose operon promoter, tryptophan operon promoter and the like have been employed as a promoter, i.e. the initiation site for transcription with RNA polymerase. In order to increase the rate of translation, various recombinants wherein the length between the Shine-Dalgarno sequence (referred to as SD sequence hereinafter) and the initiation site of the translation is varied, generally 3 to 15 base pairs, have been prepared. See Keiichi Itakura, Science 198, 1056-1063 (1977); A. H. Seeburg et al.: Nature 276, 795-798 (1978) and J. A. Martial et al.: Science 205, 602-607 (1979). As a practical problem, however, with use of the examples mentioned above, proteins are generally produced as fused proteins consisting of two or more proteins. Although the direct production of intact proteins has been reported by David V. Goeddel et al.: Nature, 281, 544-548 (1979); Goeddel et al.: Nature, 287, 411-416 (1980) and Goeddel et al.: Nucleic Acid Research, 8, 4057-4074 (1980), the method of direct production is inconvenient because a special synthetic DNA is used as a joint to insert the foreign gene together with the initiation codon ATG for translation downstream from the promotor. Thus, a need exists for an efficient and industrially applicable method for synthesis of a polypeptide coded by a foreign gene in a microorganism. To this end, vectors have now been constructed which overcome the deficiencies of the known plasmid vectors and which are useful particularly for efficient expression of IFN-.beta. in Escherichia coli.